2,130 research outputs found
Glass-like dynamical behavior in hierarchical models submitted to continuous cooling and heating processes
The dynamical behavior of a kind of models with hierarchically constrained
dynamics is investigated. The models exhibit many properties resembling real
structural glasses. In particular, we focus on the study of time-dependent
temperature processes. In cooling processes, a phenomenon analogous to the
laboratory glass transition appears. The residual properties are analytically
evaluated, and the concept of fictive temperature is discussed on a physical
base. The evolution of the system in heating processes is governed by the
existence of a normal solution of the evolution equations, which is approached
by all the other solutions. This trend of the system is directly related to the
glassy hysteresis effects shown by these systems. The existence of the normal
solution is not restricted to the linear regime around equilibrium, but it is
defined for any arbitrary, far from equilibrium, situation.Comment: 20 pages, 7 figures; minor changes, accepted in Phys. Rev.
Closed model for granular compaction under weak tapping
A one dimensional lattice model is formulated to study tapping dynamics and
the long time steady distribution in granular media. The dynamics conserves the
number of particles in the system, and density changes are associated to the
creation and destruction of empty sites. The model is shown to be consistent
with Edwards thermodynamics theory of powders. The relationship with lattice
models in which the number of particles is not conserved is discussed.Comment: 18 pages in revtex preprint style, 4 figures; Phys. Rev. E (in press
Dissociation of place preference and tolerance responses to sucrose using a dopamine antagonist in the planarian
In rodents, sucrose has been found to elicit addictive-like behaviours like the development of tolerance and the association with cues present at the time of consumption. Furthermore, the neurochemical response to sucrose binges is equivalent to the one observed in response to the abuse of addictive substances like cocaine. The experiments reported here address the effects of sucrose on an invertebrate model, the Platyhelminth brown planarian. The animals exposed to a 10% sucrose solution in one context developed a conditioned place preference (CPP) which was subsequently extinguished in the absence of the rewarding agent. However, one exposure to sucrose per se sufficed to reinstate the CPP response, suggesting sucrose-induced CPP can be characterised as a standard Pavlovian response. The same training procedure led to the development of context-specific tolerance to the effects of sucrose. However, comparing animals treated with dopamine D1 antagonist (SCH-23390) with control animals
showed that the establishment of CPP, but not the development of tolerance, is mediated by the dopamine reward system
Analytical solution of a one-dimensional Ising model with zero temperature dynamics
The one-dimensional Ising model with nearest neighbour interactions and the
zero-temperature dynamics recently considered by Lefevre and Dean -J. Phys. A:
Math. Gen. {\bf 34}, L213 (2001)- is investigated. By introducing a
particle-hole description, in which the holes are associated to the domain
walls of the Ising model, an analytical solution is obtained. The result for
the asymptotic energy agrees with that found in the mean field approximation.Comment: 6 pages, no figures; accepted in J. Phys. A: Math. Gen. (Letter to
the Editor
Adsorption of a binary mixture of monomers with nearest-neighbour cooperative effects
A model for the adsorption of a binary mixture on a one-dimensional infinite
lattice with nearest neighbour cooperative effects is considered. The particles
of the two species are both monomers but differ in the repulsive interaction
experienced by them when trying to adsorb. An exact expression for the coverage
of the lattice is derived. In the jamming limit, it is a monotonic function of
the ratio between the attempt frequencies of the two species, varying between
the values corresponding to each of the two single species. This is in contrast
with the results obtained in other models for the adsorption of particles of
different sizes. The structure of the jamming state is also investigated.Comment: v2: Errors in the figures fixed; same text; 23 pages, 5 figures.
Accepted for publication in Journal of Physics A: Mathematical and Genera
Memory effects in vibrated granular systems
Granular materials present memory effects when submitted to tapping
processes. These effects have been observed experimentally and are discussed
here in the context of a general kind of model systems for compaction
formulated at a mesoscopic level. The theoretical predictions qualitatively
agree with the experimental results. As an example, a particular simple model
is used for detailed calculations.Comment: 12 pages, 5 figures; to appear in Journal of Physics: Condensed
Matter (Special Issue: Proceedings of ESF SPHINX Workshop on ``Glassy
behaviour of kinetically constrained models.''
Scaling and aging in the homogeneous cooling state of a granular fluid of hard particles
The presence of the aging phenomenon in the homogeneous cooling state (HCS)
of a granular fluid composed of inelastic hard spheres or disks is
investigated. As a consequence of the scaling property of the -particle
distribution function, it is obtained that the decay of the normalized two-time
correlation functions slows down as the time elapsed since the beginning of the
measurement increases. This result is confirmed by molecular dynamics
simulations for the particular case of the total energy of the system. The
agreement is also quantitative in the low density limit, for which an explicit
analytical form of the time correlation function has been derived. The reported
results also provide support for the existence of the HCS as a solution of the
N-particle Liouville equation.Comment: 17 pages, 3 figures; v3 revised version (minor changes, corrected
typos, v2=v1 due to a submission error)accepted for publication in J. Phys.
A: Math. Theo
Seguridad e higiene en la práctica saludable del Acrosport
La inclusión de habilidades gimnásticas en la programación de los docentes de Educación Física en centros educativos ha sido hasta hace algún tiempo bastante frecuente. Sin embargo, numerosos docentes afirman que cada vez son más reticentes a la realización de este tipo de habilidades por la existencia para ellos de un mayor riesgo de lesión para sus alumnos y por los problemas que podría acarrearles si ello ocurriese de forma más o menos grave. Esta comunicación pretende facilitar consideraciones metodológicas concretas a los profesores de Educación Física de alumnos en edad escolar, para aumentar aspectos relacionados con la prevención de lesiones e higiene en la práctica deportiva saludable en este tipo actividades, no implicando necesariamente mayor riesgo que cualquier otra actividad tradicional realizada
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